Graphical modeling environments may allow a user to develop, analyze, and simulate graphical computer models of real-world systems. A graphical model may include a number of different components and may include a hierarchical structure that includes multiple levels. For example, a top level of the graphical model may include a number of components. One or more of the components in the top level may be a component that references a subsystem. The subsystem may also include multiple components, at least one of which may also reference another subsystem.